This investigation establishes a likely order of magnitude for the zero-time correction factor governing the effective time of centrifugation that is pertinent in the analysis of boundary spreading in sedimentation velocity experiments. This correction is shown to be too small to unduly affect the magnitudes of sedimentation and diffusion coefficients deduced from the application of computer software incorporating the printout value of ω2t and an effective position of the air–solution meniscus that is obtained as an additional parameter in the analysis involving nonlinear least-squares curve-fitting of sedimentation velocity distributions to the Lamm equation. Although this procedure slightly underestimates the actual meniscus position (ra), uncertainty about its exact location precludes adoption of the alternative approach with rafixed and the correction to ω2t regarded as the additional curve-fitting parameter.